Studies of methane-oxidation kinetics

Abstract

Following a brief evaluation of published rate constants for the initiation steps in methane oxidation, we present new results on methane pyrolysis using methane emission and also methane-absorption data obtained with a He−Ne laser beam at 3.392 μ. Our, rate-constant estimate for CH4 decomposition agrees well with previously published values of Hartig et al and of Roth and Just, thus removing a large existing uncertainty in this number. Substantially equivalent data are obtained for ignition delays using any one of the following emitters: OH, CH, C2, CO+O, CO, or H2O. Our ignition delays for CH4−O2−Ar mixtures correlate reasonably well with earlier results obtained below 2,200°K but are relatively lower at higher temperatures. The CO+O recombination radiation has been used to estimate the concentration product (CO)(O). Our results agree with earlier work by Jachimowski. Absolute concentration levels have been measured for excited states of OH, CH and C2 and show expected non-equilibrium populations. Concentration ratios for electronically excited states of CH and C2 with respect to OH are frequently greater than unity. The kinetic implications of these findings have not been investigated.